MOTION CONTROL SYSTEMS

Abstract: The motion of a member such as a simulator plane (40) and a "virtual reality" cabin, or a vehicle, is controlled by apparatus comprising one or more preferably electromagnetic actuators (30) disposed between the member (40) and a ground level (10), and a control arrangement for providing signals to the actuator whereby to cause the actuators to generate thrust. In order to allow the motion of the member (40) to be influenced by factors such as the movement of a user on the simulator plane, or the detection of other movements, the apparatus further comprises means for monitoring characteristic of the relative positions or movements of the member and the ground level (10) or the forces between the ground level, the actuator and the member, and providing signals indicative of said characteristics. The control arrangement is responsive to signals provided by the monitoring means and comprises means for generating or modifying the control signals to be provided to the actuator. By controlling the motion of a member in this way, it is possible to make motion systems such as "virtual reality" system more convincing. It is also possible to construct stabilizing systems such as active suspension systems (85) for vehicles.

Description: MOTION CONTROL SYSTEMS The present invention relates to an apparatus for controlling the motion of an object. In particular it relates to motion control apparatus wherein forces are generated by actuators such as electromagnetic actuators having a piston and a cylinder and in which relative motion is caused to happen between the piston and the cylinder by means of electromagnetic force- Examples of such electromagnetic rams are disclosed in International Patent Application No. PCT/GB92/01277, published as WO 93/01646. The present invention also relates to a corresponding method for controlling the motion of an object or objects by means actuators such as for example, electromagnetic actuators. The present invention has applications in the field of motion simulation. Motion simulators are now used in, for example, flight simulators for training pilots, and in arcade games based on activities such as motor-cycle racing. In these examples, motion simulation is generally enhanced by the provision of audio visual signals to the user in order to make the experience of actual motion seem more realistic. Such motion simulators are now known to the general public as "virtual reality" machines and are becoming more widely available for recreational and educational uses. In general motion simulators are known which utilize hydraulic or pneumatic rams as the actuators providing the necessary forces to move a user who may be in a simulator cabin or on a simulator plane. More recently it has been proposed by the inventor of the present application to utilize electromagnetic actuators as the thrust producers in motion simulation devices (see, for example, International Application PCT/GB92/01279, published as WO 93/01577). It is known for motion simulators, comprising a set of actuators arranged between a base plane and a simulator plane or cabin, to provide motion simulation according to a predetermined program, wherein each actuator operates according to predetermined time dependent functions or to stored data in order to cause a sequence of thrusts or moves to be applied to a simulator cabin or simulator plane. In this way a user on the simulator plane may experience a "virtual reality ride" around a well-known motor racing circuit or down a well-known toboggan run, for example. Such simulators may be said to provide "hard" simulation of a predetermined experience in the sense that the actuators apply set sequences of thrusts or moves to the simulator plane or cabin irrespective of any action on the part of a user in a cabin or on a simulator plane. It is also known for a user, or an external controller, to be able to control the thrusts to be applied to the cabin or simulator plane, by operation of, for example a steering wheel or a joy-stick control system. Such simulators are able to provide simulation of a non-predetermined experience, but may still be said to be providing "hard" simulation since the motion or thrusts applied to the cabin or simulator plane are still determined, albeit contemporaneously, by a computer control mechanism responsive only to external commands. A particular example of motion simulator employing a combination of the above two types of "hard" simulation would be a flight simulator in which a user in a cabin, the inside of which is intended to look and feel like a cock pit, controls an "aeroplane" by operating controls similar to those of a real aircraft. Signals from these controls are processed and applied to a set of actuators arranged to change the position and orientation of the cock pit in order that the user experiences the effects of his own control of the plane until such time as his actions, if carried out in an aeroplane, would have resulted in an unrecoverable crash. At such a time as this, the control of the actuators may be taken completely away from the user and instead, the actuators may be controlled to simulate a crash by running a predetermined sequence of moves. Irrespective of whether the flight simulator according to this example is in the first mode (i.e. under the user's control), or in the second mode (i.e. performing the predetermined "crash" routine), the simulation may be said to be "hard" on account of the fact that the actuators are only responsive to externally driven commands. It is desired to provide motion simulators in which signals provided to an actuator or to a set of actuators are determined not only from external commands but also, for example, from movement of a user in a cabin or on a simulator plane. Signals determined as a result of movement of the user may thus be provided to the actuators in addition to a predetermined sequence of signals such that the user feels that his changes in position are affecting the motion of the object whose motion is being simulated. For example in a simulator for simulating surfing on the sea, wherein a surf-board is placed on a simulator plane, the actuators may be provided with signals such that the simulator plane moves as if under the action of waves, and in addition to this, they may be provided with additional signals if a "surfer" on the surf-board shifts his weight relative to the surf-board, such that the motion of the surf¬ board is affected by the movements of the surfer. Such simulation may be referred to as "soft" simulation. According to the present invention there is provided apparatus for controlling the motion of a member, comprising an actuator disposed between the member and a ground level, and a control arrangement for providing control signals to the actuator whereby to cause the actuator to generate thrust, characterised in that said apparatus further comprises means for monitoring characteristics of the relative positions or movements of the member and the ground level or the forces between ground level, actuator and member, and providing signals indicative of said characteristics, and in that the control arrangement is responsive to signals provided by the monitoring means and comprises means for modifying or generating the control signals to be provided to the actuator. Preferred embodiments of the invention utilize electromagnetic actuators and make use of the feature of these that in addition to converting electrical signals to thrust, they may produce electrical signals directly as a result of force being applied to them. In the field of motion simulation outlined above, apparatus according to an embodiment of the present invention in general comprises a plurality of actuators disposed between a plane resting on the ground and an object on which a user may "ride". The object on which the user rides may be located on a plane which is attached to the actuators, or may be attached to the actuators itself. In order for motion simulation to be "soft" it is generally necessary for the apparatus to include means for monitoring characteristics of the position or movement of the member of a user on the member, although it may be necessary also to monitor corresponding characteristics of the ground plane in some circumstances. In motion simulators utilizing a preferred embodiment of the apparatus according to the present invention, use is preferably made of the fact that currents are generated in the coils of an electromagnetic actuator when there is relative movement between the piston and the cylinder, and by monitoring these currents, the extension or reduction of the actuators as a result of movement of the user may be monitored without the need for further connections or sensors to be mounted on the actuators. Alternatively, however movements of the user may be detected by monitoring other characteristics, such as the angles between the actuators, the lengths of the actuators, or the rate of change of extension or reduction of the length of the actuators. Also, movements of the user may be detected more directly by attaching movement sensors of any convenient type to the user or to the member, or by any other convenient means. Signals indicative of characteristics of the position of movement of the member, having been obtained by any chosen form of monitoring means, may be processed by computer control means such as to provide control signals to the actuator which are the sole control signals to the actuators. Alternatively, a predetermined sequence of control signals may be modified as a result of signals received from the monitoring means in order to "superimpose" the effects of a users movements on a predetermined ride. In either such situation, the simulated motion may be said to be "soft". As explained above, motion simulators utilizing embodiments of the present invention generally include more than one electromagnetic ram, and may also include other support means such as air springs. It is not, however, necessary for there to be a plurality of actuators, and a further application of embodiments of the present invention, in which a single actuator may suffice, will be outlined below. It is well known that spring systems and spring damper combinations can be modelled by computer and that ideal spring and/or damper systems can be designed in this way. However, when putting such computer modelling into practice it is often the case that design compromises have to be made. In the past, spring and damper combinations have been adjustable to the extent that the damper characteristics may be switched but again these are very crude systems when compared with the computer modelling which is possible. The advent of electromagnetic piston and cylinder devices capable of producing high thrusts has allowed designers to produce any desired thrust characteristic profile. We now propose utilizing the controllable aspect of an electromagnetic piston and cylinder device to drive the piston forwards and backwards at rates determined by the designer and between limit positions also determined by the designer in order to simulate a specific spring or combination of springs or combination of springs and dampers. The advantage of using an electromagnetic ram system is that because the switching of the coils which causes the relative movement between the piston and cylinder is already under computer control, it is possible to feed new programs to the computer which will alter the characteristics of the piston and cylinder device. Piston and cylinder actuators controlled according to some embodiments of the present invention as set out above may be made to act as "virtual springs", "virtual dampers" or "virtual spring/damper combinations", utilizing terminology used in the field of "virtual reality". A particular application of such embodiments is in the field of suspension systems, such as active suspension systems for vehicles. As explained above, an electromagnetic actuator controlled according to embodiments of the present invention may be controlled such that it acts as a spring or a combination of springs, a damper or a combination of dampers, or a combination of springs and dampers. In suspension systems, the aim of controlling the motion may be thought of as the reverse of that in motion simulation, since it is generally desired to allow a user a smooth a ride as possible in, for example, situations wherein a vehicle is travelling over irregular terrain. The monitoring of movement is thus principally directed to that of a base plane or a set of wheels, which may be considered to travel across the "ground level", but monitoring means similar to those described in relation to motion simulators may be used. Other applications of the present invention will become apparent from a full description of embodiments of the invention. Embodiments of the present invention will now be described with reference to the accompanying figures in which: Figure 1 shows in diagrammatical form a motion simulator of a known type which may be controlled according to an embodiment of the present invention; Figure 2 shows a perspective view of a simulator mechanism such as that shown in Fig. 1; Figure 3 shows the two principal parts of an electromagnetic actuator; Figure 4 shows a piston suitable for use in an alternative type of electromagnetic actuator; Figures 5, 6 and 7 show alternative arrangements of an electromagnetic actuator; Figure 8 shows a circuit for supplying current to, and receiving current from, an electromagnetic actuator; Figure 9 shows, in diagrammatical form, an embodiment of a motion control apparatus according to the present invention; Figure 10 shows, in diagrammatical form, an active suspension system of a car, controlled according to an embodiment of the present invention; Referring to Figure 1, there is shown in diagrammatical form a motion simulator to which an embodiment of the motion control apparatus of the present invention may be applied. A motion simulator of this type, but for "hard" simulation was the subject of International Publication WO94/10665, filed by the applicant of the present application, the subject matter of which is incorporated herein by reference. As shown, there is a base plane 10, which may rest on a floor or be otherwise stably supported, and a simulator plane 40 on which may be mounted a capsule motor-cycle, or surf-board, for example, (not shown) that is to undergo simulated motion. The capsule may represent a cabin, such as an aircraft cabin, in which a user would stay during use in order to be subjected to movement. On the base plane 10 are mounted three actuators 30 which are linearly extendible electromagnetic rams. Note that although no connections to the actuators 30 are shown in Figure 1, connections would in general be required for electrical power and signals, and possibly for fluid, as will be explained later. The actuators are mounted in such a way that each is free to rotate in direction A with one degree of freedom about a point 24 on the base plane 10. For example, the actuators 30 may be mounted by means of hinges 26 whose axes each lie in the base plane 10. In general, the axes about which the actuators are free to rotate (in the example, the axes of the hinges) can be extended so as to intersect with each other at points forming a notional triangle 20 with sides 22 on the base plane 10. This notional triangle 20 is in this embodiment an equilateral triangle. The axes of the actuators 30 intersect with the axes about which they are free to rotate at points 24 which are midpoints of the sides 22 of the triangle 20 on the base plane 10. These points 24 can be thought of as the coupling points of the actuators 30. In this example, each coupling point 24 is the midpoint of one of the sides 22 of the triangle 20. They thus form a smaller triangle within the triangle 20. On account of this, the axes of the actuators 30 diverge from points on a common line irrespective of their angular positions, this line preferably being the line perpendicular to the base plane, passing through the centroid of one or both of the triangles. Each actuator 30 may be extended or shortened in directions B by a length up to that of piston 32 which in general has a length less than or equal to the length of the actuator, but may be longer if it is extendible in stages, with for example a telescopic action or if the cylinder is open-ended and the piston is allowed to move through it. The piston 32 may be supported by a slide bearing 38, to further strengthen the structure of the simulation mechanism. The pistons 32 of the actuators 30 are each joined to a point of the simulator plane 40 by means of a universal bearing 36, the three bearings forming a notional triangle 50. This notional triangle 50 is in this case an equilateral triangle and is in the simulator plane 40. The two notional triangles 20 and 50 may be of a similar size or of different sizes, depending on the required extent of the motion and the stability required. Generally however the centre of mass of the capsule should be above the centroid of the triangle 50. In addition, the centre of mass of the capsule should be kept, to a required level of accuracy, above the centroid of the points at which the actuators are coupled to the base plane. This condition may be maintained by suitable choices of sizes and positions of the triangles 20 and 50, lengths of the actuators 30 and/or external control of the types of movements that are caused by extending and shortening the actuators. (This external control may be by physically preventing the actuators from reaching angles outside a required range, or by computer control of the lengths of the actuators according to predetermined algorithms or contemporaneous calculations.) The coupling points of the actuators 30 to the triangle 20 on the base plane 10 should thus be separated sufficiently from each other for the triangle 20 to be sufficiently large to provide a means of transferring the forces produced by the actuators to the stable base plane 10. Referring to Figure 2, there is shown a perspective view of a simulator mechanism such as that shown diagrammatically in Figure 1. Prior to explaining how a simulator mechanism such as that shown in Figs. 1 and 2 may be controlled according to the present invention, some types of electromagnetic actuator suitable for use in such a mechanism will be described with reference to Figures 3, 4, 5 and 6. Such actuators are the subject of International Publication WO 93/01646, filed by the applicant of the present invention, the subject matter of which is incorporated herein by reference. Referring to Figure 3, there are shown the two principal parts of an electromagnetic actuator, which are, respectively, the cylinder 130 and the piston 135. In this example, the cylinder 130 houses a plurality of annular coils 131 which are separated from each other by pole-piece rings 132. The piston 135 is of a suitable size to slide within the central bore bf the cylinder 130, and comprises a cylindrical steel sleeve 136 on the exterior of which are mounted a plurality of segmented windings 137. Currents in the coils 131 on the cylinder may be provided such that radial magnetic fields are produced which interact with currents in the piston coils 137, whose phase is controlled according to the position of the piston and the required thrust direction. Alternatively, currents flowing in the piston coils 137 may produce radial magnetic fields which interact with currents in the cylinder windings 131. A piston for an actuator such as this is shown in Fig. 4, in which the piston comprises a steel core 140 provided with annular pole-pieces 141 and coils 142. Alternative actuator arrangements are possible. Two further examples are shown in Figs. 5 and 6. In Fig. 5, there is shown, an actuator wherein a cylinder 191 carries a plurality of annular coils 192, and wherein a piston 190 carries radially magnetised ring-magnets 193. By applying suitable currents to the coils 192, the piston 190 may be made to experience an electromagnetic force such as to extend or shorten the actuator. In Fig. 6, however, the steel cylinder 201 carries a series of ring magnets 202 which are radially magnetised, while the piston 203 carries segmented coils 204, to which current may be applied to cause electromagnetic force to be generated such as to extend or shorten the actuator. As is evident from the above electromagnetic actuators for use in embodiments of the present invention may be of a variety of types, providing it is possible to energise coils in either the piston or the cylinder such as to generate electromagnetic forces between the coils and a magnetic system in the other one of the piston and the cylinder. The magnetic system may be a single permanent magnet, a series of permanent magnets, or one or more current-carrying coils. While the principal function of the electromagnetic actuators is to produce thrusts, it is advantageous in embodiments of the present invention if the actuators are adapted to perform the reverse operation, this being the generation of currents in coils in either the piston or cylinder as a result of relative motion between the piston and the cylinder. By virtue of this it is possible to detect slight changes in the positional relationship of the piston and the cylinder by monitoring currents in the coils. It is further possible to utilize the currents in the coils to recharge a battery, for example or to provide power for use in the apparatus. A further type of electromagnetic actuator which is suitable for use in embodiments of the present invention, will briefly be described with reference to Figure 7. A full description of the unit, and in particular its electromagnetic properties will not be given as the basic unit may be of any of the types referred to earlier or referred in our International Patent Application W093/01646, or otherwise. In this example, however the principal features of the electromagnetic ram include a cylinder 230 having stator coils 231, and piston 232 having permanent magnets 233, 234 mounted thereon. Additionally, the stator includes conductive rings 235 at either end of the stator which may be made of copper or aluminium for example, and act electrical cushions to prevent violent impact by the piston at the extremes of movement. The above description refers principally to electromagnetic actuators having a piston and a cylinder, however in certain applications of the invention it may be advantageous to utilize other types of actuators, such as rotary torque actuators. It is thus not intended that this invention is limited to systems in which piston and cylinder actuators are or systems in which the actuators are electromagnetic. In general, it is necessary for an electromagnetic ram to have means to allow fluid to pass out from the inside of the cylinder as it is compressed by the movement of the piston. In this example, ports are indicated as being connected to an air reservoir which also incorporates an air-pump. This may be used to assist the electromagnetic ram in providing large thrusts, or by controlling the fluid pressure to a required level, it may be possible for a load to be supported completely by fluid pressure, until such time as the load changes or moves. Once such a change alters the pressure from the load on the piston, the piston will move due to the pressure in the piston from the air reservoir/pump and due to the effect described above in which relative motion of the piston and cylinder will generate an electromagnetic current, it will be possible to detect the movement of the piston by virtue of the monitoring of the detected currents, and it is also envisaged that the currents generated by such relative motion may be used to supply power to the system, or may be stored for use in the system or elsewhere. A circuit for supplying current to and monitoring and/or receiving current from an electromagnetic actuator will briefly be explained with reference to Figure 8. The system comprises an electromagnetic device such as a combined actuator/damper unit 310 which is normally fed with power from an energy store 311 such as a battery via a power switching device 312. In order to provide the desired motion of the unit, the power switching device 312 is controlled by a controller 314 which pulse width modulates the supply to the actuator/damper unit 310. The energy store 311 can be re-charged, if appropriate, from an alternating supply via a rectifier 315. The actuator/damper unit 310 and drive arrangement is, thus far, as described in our International Patent Application WO93/01646. When not being supplied with power to drive the unit 310, it may be used to generate electrical power as a result of relative motion of the piston and cylinder of the unit 310. This power can be fed back to the electrical store 311, if required. The controller 314 is therefore used to control a further power switch 320 for receiving current form nit 310 and feeding it via a current transformer 312 and a rectifier 322 to the store 311. Although the above described system contemplates the damping action of the system being used to replenish an energy store for activating the actuator/damper unit, it could be used for other purposes not necessarily connected with the actuator/damper unit 310. It is preferred to use it, however, for some immediately useful purpose associated with the damped action. In the case of an air-sprung motion base, energy recovered from the unit 310 could be used to drive a compressor which charges an air reservoir, for example. An embodiment of the invention will now be described with reference to Figure 7. This shows motion control apparatus according to a preferred embodiment of the present invention, incorporating an electromagnetic actuator which may be of any suitable type as explained earlier, but in this example is of a type with current carrying coils on the cylinder. A computer control means supplies signals to a set of pulse-width modulating switches which control the supply of power to the coils in the cylinder in response to the control signals received from the computer control means. As a result of the supply of power to the coils, the piston is subjected to thrusts generated as a result of electromagnetic forces. With the features described above, the apparatus would be capable of achieving "hard" simulation. In order to allow the apparatus to provide "soft" simulation, there is provided means for sensing the relative positions of points on the cylinder and piston, or other characteristics of the actuator parts, such as the relative velocity of the piston with respect to the cylinder. The position sensing means provides signals indicative of, in this example, the relative positions of the piston and cylinder, to the computer control means, which may then modify or generate control signals to be sent to the switching means such that forces with any described relationship to the positional relationship may be produced. The response determined by the computer and control means may be determined in a variety of ways. Two simple applications of the above apparatus are as a "virtual spring", or as a "virtual damper". These illustrate manners in which the response may be decided. To simulate a conventional spring it is necessary for the restoring forces to be directly proportional to the piston displacement over a predetermined distance. This is known as the characteristic of the spring, and is summarised by the equation P = -kx, where P is the restoring force, x is the displacement from a reference point, and k is the spring constant or spring rate. A chosen spring rate is thus entered by a user, and is stored as data which is supplied to the computer control means in order that a response to a sensed positional relationship may be determined. Similarly, to simulate a conventional damper, it is necessary for the restoring force opposing the motion to be proportional to the rate of change of displacement, i.e. the velocity of a moving point relative to a reference point. This may be summarised by the equation P= -qv, where v is the velocity of the point and q is the damping coefficient. A chosen damping coefficient is thus entered by a user and is stored as data which is utilized by the computer control means in order that a response to a sensed velocity may be determined. The above two applications of the invention may be superimposed, for example, if it desired to simulate a spring and a damper in parallel, by calculating a restoring force according to the equation. P = - kx - qv. The coefficients k and q may be chosen independently, and may, for example, be chosen in accordance with the dynamic mass of the object being positioned in order to achieve critical damping. Features of actual springs which are not summarised by the principal linear relationship above include springs reaching their elastic limit and springs breaking. These features can also be imitated by a virtual spring according to an embodiment of the present invention. In order to simulate a spring reaching its elastic limit, the restoring force is made to become very large at a predetermined displacement from a reference point, such that the "spring" resists any further stretching. On the other hand, in order to simulate a spring breaking, the restoring force could suddenly be reduced to zero by reducing the spring rate to zero. It will be clear that it is possible to imitate a wide range of spring or damper characteristics, including many which are unattainable with real springs and dampers. In some applications it would be an advantage to use the apparatus as a spring whose characteristics can be changed to suit with the dynamics of the load. For example, it would be possible to tune the resonant frequency of a system whose mass is not predetermined or is actually unknown, by altering the spring rate to suit. Further, if the mass changes in time, perhaps as a result of a controlled process, the force:distance characteristic of the actuator can also be changed in real time so as to achieve the desired resonance characteristic. As explained above, a particular application of an embodiment of the preferred invention is in virtual reality motion simulators. Referring again to Figures 1 and 2, a surf-board may be placed on simulator plane 40 in order to provide "virtual-reality surfing". In the absence of a user, the actuators 30 could be supplied with signals such that the simulator plane 40 imitates the motion of a surf-board under the action of waves, either when stationary or when moving across the water. The actuators could be caused to produce regular motion or a predetermined sequence according to predetermined algorithms, or could be caused to produce random or pseudo-random motion within predefined limits, by the control means (see Fig. 9). A user climbing on board, or alternatively onto the simulator plane 40 itself, would alter the condition of the actuators and would continue to alter this whenever he moved his weight relative to the centre of gravity of the simulator plane. On detection of such changes in the condition of the actuators, as monitored by the sensing means (see Fig. 9), the control signals to each actuator could be modified by changing the algorithms by which they are controlled, or by introducing damping coefficients and spring rates, which may be time-varying, for example, as well as dependent on further changes in the position of the user on the simulator plane. By virtue of such control, the user will feel that his own movements are affecting the movement of the surf-board or simulator plane. It will be noted that in motion control systems having a plurality of actuators, it may be sufficient for the control signals to the actuators to be supplied independently, possibly by separate computer control systems, in order to cause a predetermined sequence of moves such as, for example, to simulate the effect of waves on the surfboard described above. If, however, it is desired that the motion control apparatus is to superimpose "soft" simulation effects on the predetermined "hard" simulation by detecting and responding to movements of a user, it is generally necessary for more than one sensor to monitor movements of the user. In preferred embodiments, in which movements of the user are monitored by monitoring effects on the actuators such as the generation of currents in conductive loops in the cylinders of the actuators as a result of relative motion between magnets mounted on the pistons and the conductive loops in the cylinders, it will generally be necessary for signals by some or all of the actuators to be monitored by a central computer means in order for a realistic response to be calculated. If, for example, a user moves his weight towards one of the three actuators in the simulator shown in Figs. 1 and 2, and away from the other two actuators, the first actuator may generate a "positive error signal" while the other two generate "negative error signals". It will generally be necessary to compare or analyse the three signals in order to determine new control signals. A further particular application of embodiments of the present invention is in the field of active suspension for vehicles. Cars and other vehicles generally are provided with a suspension system. A typical suspension system for a car consists of a set of components equivalent to a complex spring/damper combination, mounted between the main body of the car and the wheels. By selecting appropriate spring and damper characteristics it is possible to provide a suspension system offering two particular advantages to the driver of the car. The first of these is that the effect of sudden jolts, such as those caused when a wheel of the car encounters a bump or a hole in the road, may be absorbed by the system such as to allow the driver of the car a more comfortable ride. The second of these is that the wheels of the car may remain in contact with the road even in situations in which a car without a suspension system would temporarily lose contact with the road, such as may occur, for example, if one drives with excessive speed over a ramp. This advantage is linked to the first advantage, and additionally allows for better road-holding, leading to more effective steering and breaking, and to decrease wear and tear of the vehicle in general. Known types of suspension systems for cars and other vehicles include mechanical, hydraulic and pneumatic suspension systems. It is generally possible to adjust the spring and damper characteristic of suspension systems of vehicles. It may be necessary to stop the car in order to allow such adjustments to be made, but it is possible to adjust the suspension characteristics of some cars, and in particular those for use in motor-racing, by means of controls within the car while the car is in motion. It is thus possible to adjust the firmness of the suspension in accordance with changing road conditions, such as to allow the car to. be approximately "critically damped" as it passes over varying terrain. More recently, and in particular in the field of motor-racing, a type of suspension known as "active suspension" has been developed. With active suspension, the spring and damper characteristics of the suspension system are adjusted automatically in response to detected changes in driving conditions, such as changes in steering, tilting of the car due to irregular or cambered road surfaces, changes in the distribution and/or amount of mass being carried by the car, and other changes. A typical aim of an active suspension system is to alter the spring and damper characteristic continuously as the vehicle moves over a surface having a variety of irregularities, such as to maintain the system in a condition of critical damping, the spring and damper characteristics being set and altered in response to detected changes in driving conditions, without the need for the driver to provide direct commands to the suspension system. Known active suspension systems in motor-racing generally utilize a hydraulically damped suspension system in which the hydraulic pressure or the volume of water in the system is altered as a result of the detection of changes in driving conditions. Such changes may be detected by means of strain gauges attached to the wheel support structure, or otherwise. Referring now to Figure 10, a suspension system of a car is shown in diagrammatic form. The diagram indicates a front view of a car, and illustrates only those features of relevance to an explanation of an active suspension system. The car body indicated by box 60 is linked to a steering box 70 by steering column 65, which communicates steering commands provided to it by a steering control means 62 to the steering box 70. These commands may be electronic, mechanical, hydraulic or pneumatic signals, or may be other types of signals. The steering box 70 is linked to the front wheels 80 by supports 75 via axles 78, the supports being movable in response to steering commands such as to alter the axis of rotation of the wheels and thus to change the direction of the car. Between the body of the car 60 and the wheel supports 75 are suspension systems 85, shown in this diagram as piston and cylinder systems. The suspension systems 85 are shown as being controlled by suspension control systems 82. The suspension control systems 82 need not be within the car body 60. Further there may be a single suspension control system 82 controlling all of the suspension systems, or there may be a suspension control system for each suspension system or for each pair of suspension systems, for example. Sensors of a variety of types, such as strain gauges, may be mounted within the support structures 75 or elsewhere in order to detect changes in driving conditions such as irregularities in the road surface 95. In the diagram, these sensors are indicated as strain gauges 76 mounted on a leaf spring 77, the strain gauges being connected electrically to the suspension control means 82 by connection means which are not shown. The suspension systems 85 may initially be controlled to act as spring/damper combinations having predetermined spring/damper characteristics that approximate to, for example critical damping for the car moving at an average speed over an averagely bumpy road while carrying an average load. The spring/damper characteristics may be adjusted such as to provide critical damping under changed conditions by providing different signals from the suspension control systems 82, which may be hydraulic signals if the suspension systems are hydraulic. In order for the suspension to be considered "active suspension" however, the suspension systems 85 must be controlled in a manner determined at least partially from the results of the detection of a characteristic of the driving conditions, such as for example, irregularities in the surface over which the wheels are travelling, or changes in the steering direction of the wheels. The control of the suspension systems 85 may be the alteration of the damping factor, which may be done for example at regular intervals, or wherever a change above a threshold level is detected, or continuously. Alternatively the control may be of the length of the piston and cylinder assembly. With control of this type, it may be possible to maintain the car body at a predetermined absolute height irrespective of any holes or bumps encountered by the wheels 80 by adjusting the length between the car body 60 and the support structures 75 in response to the estimated size of each irregularity. Other types of control, with alternative aims, utilizing the concept of monitoring driving conditions and controlling the suspension system accordingly, will be apparent. The applicability of the present invention to the field of suspension systems and to active suspension systems in particular, stems in part from the speed and accuracy with which electromagnetic rams may be controlled. It also stems in part from the fact that suitably constructed actuators, preferably electromagnetic, may serve not only as force generators, but also as sensors of their own motion as a result of other forces. Referring again to Figure 10, if each suspension system 85 contains an electromagnetic ram, the support structures 75 or the wheels 80 are considered to be on a notional "ground level", and the car body 60 is considered to be the member whose motion it is intended to control. It will be noted that in contrast to the field of motion simulation, in which the intention is to cause a member to move in relation to a stably mounted ground plane, in the field of active suspension it is generally intended to decrease the motion of a member such as a car body in spite of the motion of a ground plane such as a wheel or support structure, caused for example by a wheel rolling over a hole or a bump in the road. Utilizing suitably constructed electromagnetic actuators in the suspension systems 85, characteristics of the relative motion between the car body 60 and the support structures 75 may be monitored by detecting currents generated in the electromagnetic components of the pistons or cylinders of the electromagnetics rams. Signals indicative of those generated currents may then be supplied (by connection means not shown in Figure 10) to the suspension control means 82 which are thus able to alter the spring and damper characteristics or other characteristics of the suspension systems 75 in accordance with predetermined functions of the signals or in accordance with other data dependent on the conditions of the electromagnetic rams. It is thus possible to dispense with the independent sensor systems 76,77 while still allowing for sufficient monitoring of driving conditions to enable active suspension to be provided. In fact, by monitoring the signals from the electromagnetic rams instead of those from independent sensors, it is generally possible to monitor characteristics more directly indicative of relative motion between the car body 60 and the wheels 80 or support structures 75, and thus to monitor relevant characteristics of driving conditions more directly. It is thus preferable that the "error signals" are produced by the actuators themselves in this manner, but it is envisaged that the error signals may be produced to other ways according to other embodiments of the invention. In addition to the fields of motion simulation and suspension systems, it is envisaged that embodiments of the present invention will have applications in many other fields. Utilizing the particular advantages of electromagnetic actuators over most types of force generator it is foreseeable that embodiments of the present invention will have applications, in particular, in situations in which people and objects must be moved, or stabilized despite movement of their support, wherein the control of motion depends in some way on the detection of characteristics within or outside the system. For example, if electromagnetic rams are used as the force-generators in elevators, characteristics such as changes in the total weight of the passengers in the lift as people enter and exit the lift could be monitored, thus allowing the control signals to the rams to be altered according to such changes. Transport of delicate objects which may be damaged by jolts may be effected very smoothly by use of suitably controlled electromagnetic rams. The particular advantages of electromagnetic actuators have been explained above. These stem in particular from the feature that in addition to being able to produce thrusts when energized by a suitable electrical signal, they are also able to produce electrical signals directly when subjected to forces which cause relative motion between the components of the actuator. Embodiments of the present invention are not limited to those utilizing electromagnetic actuators, however. Other types of actuators, such as for example ball-screw actuators may be used, having means within or thereon with which to monitor characteristics of the relative positions or movements of the member and the ground level, or the forces between the ground level, the actuator and the member, in order to obtain signals from which to estimate or calculate movements, or changes in the forces applied to the system. It is foreseeable that sensors able to monitor forces, independently of monitoring any relative motion between the actuator components, may be used.

Claims: CLAIMS : 1. Apparatus for controlling the motion of a member, said apparatus comprising an actuator disposed between the member and a ground level and a control arrangement for providing signals to the actuator whereby to cause the actuator to generate thrust, characterised in that said apparatus further comprises means for monitoring characteristics of the relative positions or movements of the member and the ground level or the forces between the ground level, actuator and member, and providing signals indicative of said characteristics, and in that said control arrangement is responsive to signals provided by the monitoring means and comprises means for generating or modifying the control signals to be provided to the actuator. 2. Apparatus according to claim 1, wherein said actuator comprises a piston and a cylinder. 3. Apparatus according to claim 2, wherein said monitoring means is for monitoring characteristics of the relative positions or movements of the piston and the cylinder. 4. Apparatus according to claim 1, 2 or 3 wherein the actuator is an electromagnetic actuator. 5. Apparatus according to claim 2, 3 or 4, wherein said monitoring means is for monitoring electrical signals generated as a result of relative movement between a magnetic element mounted on the piston and an electrically conductive circuit mounted on the cylinder. 6. Apparatus according to claim 2, 3 or 4, wherein said monitoring is for monitoring electrical signals generated as a result of relative movement between a magnetic element mounted on the cylinder and an electrically conductive circuit mounted on the piston. 7. Apparatus according to claim 5 or 6, wherein said magnetic element is a permanent magnet. 8. Apparatus according to claim 5 or 6, wherein said magnetic element is an electrically conductive circuit. 9. Apparatus according to any of the preceding claims wherein said control arrangement comprises means for providing a predetermined sequence of control signals to the actuator whereby to cause the actuator to generate a predetermined sequence of thrusts. 10. Apparatus according to claim 9, wherein said control arrangement further comprises means for modifying said predetermined sequence of control signals in response to signals received from the monitoring means, whereby to modify the thrusts generated by the actuator. 11. Apparatus according to any of claims 1 to 10, wherein said control arrangement comprises means for providing control signals according to a predetermined function of the signals received from the monitoring means. 12. Apparatus according to claim 11, wherein said predetermined function is such that the control signals cause the actuator to generate thrusts which are a function of change in the relative positions of the member and the ground level. 13. Apparatus according to claim 12, wherein said predetermined function is such that the control signals cause the actuator to generate thrusts which are proportional to the relative displacement of the member and the ground level from a predetermined equilibrium displacement. 14. Apparatus according to claim 11, 12 or 13 wherein said predetermined function is such that the control signals cause the actuator to generate thrusts which are a function of the rate of change of the relative positions of the member and the ground level. 15. Apparatus according to claim 14, wherein said predetermined function is such that the control signals cause the actuator to generate thrusts which are proportional to the rate of change of the relative positions of the member and the ground level. 16. A motion control system comprising one or more actuators disposed between a ground level and a member, said motion control system comprising apparatus according to any of claims 1 to 15 for causing the or each actuator to generate thrust. 17. A motion control system according to claim 16, wherein a lower end of the or each actuator is mounted on a stable base. 18. A motion control system according to claim 17 wherein a movable surface is mounted on an upper end of the or each actuator, whereby thrusts generated by the or each actuator cause motion of the surface. 19. A motion control system according to claim 18 wherein motion of the surface causes forces to be applied to the or each actuator. 20. A motion control system according to claim 16 wherein a lower end of the or each actuator is mounted on a means for moving said system across a surface. 21. A motion control system according to claim 20 wherein forces applied to said moving means are communicated to the or each actuator. 22. A motion control system according to any of claims 16 to 21 wherein the control means is for controlling the or each actuator such as to minimize or stabilize forces applied to the member. 23 A motion control system according to any of claims 16 to 22 wherein the or each actuator is an electromagnetic actuator. 24. A motion control system according to any of claims 16 to 23, comprising a plurality of actuators, monitoring means for monitoring characteristics of position or movement of each actuator and providing signals indicative of said characteristics to a common control arrangement being responsive to said signals and having means for generating or modifying control signals to be provided to each actuator. 25. A motion control system according to any of claims 16 to 24 wherein said control arrangement comprises means for providing a predetermined sequence of control signals to the or each actuator. 26. A motion control system according to any of claims 16 to 25 wherein said control arrangement comprises means for providing control signals to the or each actuator in response to signals received from an external control means. 27. A motion control system according to any of claims 16 to 26 wherein said control arrangement comprises means for providing random or pseudo-random control signals to the or each actuator. 28. A motion control system according to claims 25, 26 or 27 wherein said control means further comprises means for altering said control signals in response to signals received from said monitoring means. 29. A suspension system comprising a motion control system according to any of claims 16 to 24. 30. A method of controlling the thrust generated by an actuator disposed between two members comprising steps of monitoring characteristics of the relative positions or movements of the members, or of the forces between the members, and providing signals indicative of said characteristics to a control means, whereby said control means generates or modifies control signals in response to signals from the monitoring means and supplies said control signals to said actuator, said actuator generating thrust in accordance with said contro1 signa1s. 31. A method according to claim 30 wherein said actuator is an electromagnetic actuator.

Inventors: DENNE PHILLIP RAYMOND MICHAEL, WATTS MARTIN PAUL, DENNE, PHILLIP, RAYMOND, MICHAEL, WATTS, MARTIN, PAUL
Applicants: DENNE DEV LTD, DENNE PHILLIP RAYMOND MICHAEL, WATTS MARTIN PAUL, DENNE DEVELOPMENTS LIMITED, DENNE, PHILLIP, RAYMOND, MICHAEL, WATTS, MARTIN, PAUL
Application year: 1994
Main classification: G09B9
IPC codes: A63G31, B60G17, G09B9